Overview
This project deals with the comparison and implementation of approaches of self-explaining roads. It mainly aims to bridge the gap between fundamental knowledge concerning self-explaining roads and the practical, hands-on knowledge that road authorities require to make their roads safer by applying the concept of self-explaining roads. The starting point is the relevant fundamental knowledge that exists on different approaches to self-explaining roads, which will be compared and evaluated.
Subsequently, this project illustrates two feasible steps towards a useful checklist that road authorities in different European countries can use, which will enhance transnational benefits. These steps will be piloted in different European countries, so as to advance towards a common European approach to self-explaining roads. The first step focuses on ascertaining road users' ability to recognise specific categories of roads and understand their context. In the second step, these results will be implemented in the development of a decision support tool for road authorities. This tool will essentially be a checklist road authorities can use to determine the extent to which their roads are self-explaining, but also contains information concerning design elements that can help to make roads more selfexplaining. As road authorities are the target group, they will be actively involved throughout this project, quite specifically in assessing the feasibility of the pilots we propose and they will also play a significant role in the dissemination process.
Results
Self-explaining roads were developed to increase inherent road safety by taking into account the nature of human perception and information processing. However, to increase road safety, self-explaining roads per se are not enough. Additionally, the entire road categorisation has to be self-explaining. With traditional road categorisation being the result of historical developments and sometimes dating back to the time when traffic safety was no major concern, this will not always be the case.
In order to allow a common and modern, state-of-the-art approach to self-explaining road categorisation to be developed in Europe, the current practice of road categorisation must be reviewed and compared with respect to its self-explaining properties. To achieve this aim, the report is structured into different parts.
Previous research has focused on the impact of different design elements on speeding behaviour, but it is less clear how universal these effects are. This was the focus of an online questionnaire study for the ERASER ERANET-roads project on self-explaining roads. It was conducted simultaneously in 6 European countries (N=307): Austria, Germany, the Netherlands, Great Britain, Ireland and Sweden. In total, 24 pictures of rural roads were presented; each a different combination of road width, separation of driving direction, vegetation of the roadside environment and the number of lanes per direction. Participants indicated their own driving speed as well as a safe speed limit on these roads. Results indicated that there are particular road features whose effects could be considered relatively self-explaining in the purest sense as they are similar for all countries (road width and vegetation). Effects of other road features, (lanes and type of separation) differed per country. This implies that extra communication (e.g. in an information campaign) or complementing roads with more self-explaining features, might enhance the desired speed behaviour.
Also in this project, a system for automated video analysis was used to collect the actual driving speed data for validation purposes. Two sites at a 2+1 road in southern Sweden were filmed using several cameras in order to be able to cover longer sections (200 and 100 m respectively). The video analysis system was adjusted so that the data from each individual camera could be connected into continuous speed profiles. Comparison with the questionnaire answers for the same road design showed good correspondence between the stated and actual driving speeds.
A tool has been developed within ERASER Work Package 3 (Road authorities pilot) to help European road authorities make decisions to improve the safety and ‘self-explainingness’ of their roads.
For this tool, the concept of self-explaining roads (SER) has been taken forward in relation to speed: the design of a road can provide explicit cues to road users about what the speed limit might be, and may also implicitly and intuitively evoke a sense of appropriate speed. It is suggested that various characteristics of a road may act as accelerators or decelerators, giving road users the impression of a faster or slower road; a self-explaining road will have characteristics that are in line with the speed limit on the road and the speed limit will therefore be credible.
The aim of the tool is not just to make roads and their speed limits more credible or self explaining, but also to ensure that speed limits are safe. The tool is grounded in the ‘safe system’ approach. In Sweden and the Netherlands, where the safe system approach has already been embraced, ‘safe’ speeds have been defined in order to improve the ‘system’ such that crashes are survivable.
The tool that has been developed requires that road characteristic data are entered and, on this basis, the tool calculates what would be a ‘safe speed’ (i.e. survivable) and assesses whether the speed limit is credible.